รบกวนช่วยแก้โค้ดจุดนี้ "gr.DrawEllipse(p_r, 0 + (c *a), 0 + ((10 * b1 )), r, r);" ให้หน่อยคับ

using System;
using System.Linq;
using System.Text;
using System.Data;
using System.Drawing;
using System.Windows.Forms;
using System.ComponentModel;
using System.Drawing.Drawing2D;
using System.Collections.Generic;

namespace Overlap
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        //private const float WorldWidth = 1000;
        //private const float WorldHeight = 1000;

        // The scale.
        //:::private float PictureScale = 1.0f;
        


        private void button1_Click(object sender, EventArgs e)
        {
            this.Cursor = Cursors.WaitCursor;
            Application.DoEvents();

            float i = float.Parse(textBox2.Text);
            float j = float.Parse(textBox1.Text);
            float iwide = float.Parse(textBox3.Text);


            Bitmap bm = new Bitmap(picCanvas.ClientSize.Width, picCanvas.ClientSize.Height);
            picCanvas.Image = bm;


            using (Graphics gr = Graphics.FromImage(bm))
            {
                gr.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;
                DrawImage(gr, i, j, iwide);
            }
            
            
            this.Cursor = Cursors.Default;
            

        }
        void DrawImage(Graphics gr, float i, float j, float iwide)
        {

            gr.Clear(picCanvas.BackColor);

            gr.PageUnit = GraphicsUnit.Millimeter;
            Pen p = new Pen(Color.Black, 1);
            Pen pp = new Pen(Color.Blue, 0.01f);
            Pen p_r = new Pen(Color.Red, 0.5f);
            
            gr.DrawRectangle(p, 0,0, i, j);
 
            float jj, jja, r = 10;
            float x1 = 0, y1 = 0,jjj;
            
            jj = (j  / 10) - 1;
            jja = (i  / 10) - 1;
            float a, b1, c, d,b2,A1,aaa,b3;
            c = iwide;
            aaa=i/c;
            A1 =(i-aaa)/c ;
            b2 = i - aaa;
          
            jjj = (j / 2);
            for (a = 0; a <= aaa-1; a++)
            {
                for (b1 = 0; b1 <= (j / r) - 1; b1++)
                {

                    gr.DrawEllipse(p_r, 0 + (c *a), 0 + ((10 * b1 )), r, r);//ช่วยแก้จุดนี้ให้หน่อยคับ 
                }
               
            } 

            float k;
            k = (i / 10) - 0;
            for (iwide = 1; iwide <= k; iwide++)
            {
                
                Pen pen = new Pen(Color.Black, 0.0005F);
                pen.DashStyle = System.Drawing.Drawing2D.DashStyle.Dash;

                gr.DrawLine(pen, x1 + (iwide * 10) - 5, y1 + j, x1 + (iwide * 10) - 5, y1);
                gr.DrawLine(pen, x1 + (iwide * 10) - 5, y1 + j, x1 + (iwide * 10) - 5, y1);
            }

            gr.Dispose();
        }
        public object PP { get; set; }

    }
}